When --noUnusedLocals/--noUnusedParameters is disabled, add suggestions instead of errors (#22361)

* When --noUnusedLocals/--noUnusedParameters is disabled, add suggestions instead of errors

* Improve performance: do not add unused suggestion diagnostics unless asking for a suggestion

* Add "unused" flag to diagnostics

* Code review

* reportsUnused -> reportsUnnecessary

* Fix test

Author: Andy

src/compiler/checker.ts

@@ -1606,6 +1606,7 @@ namespace ts {
             messageText: text,
             category: message.category,
             code: message.code,
+            reportsUnnecessary: message.unused,
         };
     }
 
@@ -1635,7 +1636,8 @@ namespace ts {
 
             messageText: text,
             category: message.category,
-            code: message.code
+            code: message.code,
+            reportsUnnecessary: message.unused,
         };
     }
 
@@ -1647,7 +1649,7 @@ namespace ts {
 
             code: chain.code,
             category: chain.category,
-            messageText: chain.next ? chain : chain.messageText
+            messageText: chain.next ? chain : chain.messageText,
         };
     }
 

src/compiler/core.ts

@@ -3282,7 +3282,8 @@
     },
     "'{0}' is declared but its value is never read.": {
         "category": "Error",
-        "code": 6133
+        "code": 6133,
+        "unused": true
     },
     "Report errors on unused locals.": {
         "category": "Message",
@@ -3302,7 +3303,8 @@
     },
     "Property '{0}' is declared but its value is never read.": {
         "category": "Error",
-        "code": 6138
+        "code": 6138,
+        "unused": true
     },
     "Import emit helpers from 'tslib'.": {
         "category": "Message",
@@ -3514,7 +3516,8 @@
     },
     "All imports in import declaration are unused.": {
         "category": "Error",
-        "code": 6192
+        "code": 6192,
+        "unused": true
     },
     "Found 1 error.": {
         "category": "Message",
@@ -3602,7 +3605,8 @@
     },
     "Unused label.": {
         "category": "Error",
-        "code": 7028
+        "code": 7028,
+        "unused": true
     },
     "Fallthrough case in switch.": {
         "category": "Error",

src/compiler/diagnosticMessages.json

@@ -4069,6 +4069,7 @@ namespace ts {
         category: DiagnosticCategory;
         code: number;
         message: string;
+        unused?: {};
     }
 
     /**
@@ -4090,6 +4091,8 @@ namespace ts {
         length: number | undefined;
         messageText: string | DiagnosticMessageChain;
         category: DiagnosticCategory;
+        /** May store more in future. For now, this will simply be `true` to indicate when a diagnostic is an unused-identifier diagnostic. */
+        reportsUnnecessary?: {};
         code: number;
         source?: string;
     }

src/compiler/types.ts

@@ -2577,7 +2577,7 @@ Actual: ${stringify(fullActual)}`);
             }
             const range = ts.first(ranges);
 
-            const codeFixes = this.getCodeFixes(fileName, errorCode, preferences);
+            const codeFixes = this.getCodeFixes(fileName, errorCode, preferences).filter(f => f.fixId === undefined); // TODO: GH#20315 filter out those that use the import fix ID;
 
             if (codeFixes.length === 0) {
                 if (expectedTextArray.length !== 0) {

src/harness/fourslash.ts

@@ -123,13 +123,14 @@ namespace ts {
         }
         {
             const actual = parseJsonConfigFileContent(json, host, basePath, existingOptions, configFileName, resolutionStack);
-            expected.errors = expected.errors.map<Diagnostic>(error => ({
+            expected.errors = expected.errors.map((error): Diagnostic => ({
                 category: error.category,
                 code: error.code,
                 file: undefined,
                 length: undefined,
                 messageText: error.messageText,
                 start: undefined,
+                reportsUnnecessary: undefined,
             }));
             assertParsed(actual, expected);
         }

src/harness/unittests/matchFiles.ts

@@ -4068,7 +4068,7 @@ namespace ts.projectSystem {
             const folderPath = "/a/b/projects/temp";
             const file1: FileOrFolder = {
                 path: `${folderPath}/a.ts`,
-                content: 'import f = require("pad")'
+                content: 'import f = require("pad"); f;'
             };
             const files = [file1, libFile];
             const host = createServerHost(files);

src/harness/unittests/tsserverProjectSystem.ts

@@ -353,11 +353,11 @@ namespace ts.server {
             return this.getDiagnostics(file, CommandNames.SuggestionDiagnosticsSync);
         }
 
-        private getDiagnostics(file: string, command: CommandNames) {
+        private getDiagnostics(file: string, command: CommandNames): Diagnostic[] {
             const request = this.processRequest<protocol.SyntacticDiagnosticsSyncRequest | protocol.SemanticDiagnosticsSyncRequest | protocol.SuggestionDiagnosticsSyncRequest>(command, { file, includeLinePosition: true });
             const response = this.processResponse<protocol.SyntacticDiagnosticsSyncResponse | protocol.SemanticDiagnosticsSyncResponse | protocol.SuggestionDiagnosticsSyncResponse>(request);
 
-            return (<protocol.DiagnosticWithLinePosition[]>response.body).map(entry => {
+            return (<protocol.DiagnosticWithLinePosition[]>response.body).map((entry): Diagnostic => {
                 const category = firstDefined(Object.keys(DiagnosticCategory), id =>
                     isString(id) && entry.category === id.toLowerCase() ? (<any>DiagnosticCategory)[id] : undefined);
                 return {
@@ -366,7 +366,8 @@ namespace ts.server {
                     length: entry.length,
                     messageText: entry.message,
                     category: Debug.assertDefined(category, "convertDiagnostic: category should not be undefined"),
-                    code: entry.code
+                    code: entry.code,
+                    reportsUnnecessary: entry.reportsUnnecessary,
                 };
             });
         }

src/server/client.ts

@@ -455,6 +455,8 @@ namespace ts.server.protocol {
         endLocation: Location;
         category: string;
         code: number;
+        /** May store more in future. For now, this will simply be `true` to indicate when a diagnostic is an unused-identifier diagnostic. */
+        reportsUnnecessary?: {};
     }
 
     /**

src/server/protocol.ts

@@ -588,6 +588,7 @@ namespace ts {
         length: number;
         category: string;
         code: number;
+        unused?: {};
     }
     export function realizeDiagnostics(diagnostics: ReadonlyArray<Diagnostic>, newLine: string): RealizedDiagnostic[] {
         return diagnostics.map(d => realizeDiagnostic(d, newLine));